Computer assistred tomography (CT), together with three dimensional image reconstruction procedures, in patients with dementia of the Alzheimer type (DAT), demonstrated that the volume of cerebrospinal fluid was larger than in age and sex matched control subjects, and that the volume of gray matter was smaller. Ventricular enlargement in the male DAT patients corresponds to the severity of dementia. In healthy subjects, men had larger volumes of cerebrospinal fluid in third and lateral ventricles than did women. Volumetric CT analysis demonstrated no differences, as compared with age matched controls, in brain morphometrics for adults withs autism and for young adults with Down syndrome (after data were normalized to body height). In male DAT patients, mean rates of enlargement of third ventricle volume and of total lateral ventricular volumes differed signifcantly from zero and from respective control values. There was no overlap between the rates of lateral ventricular enlargement in patients and controls. The rate of neuropsychological decline correlated with the rate of enlargement of the third ventricle and the right lateral ventricle.